It is unnecessary to always wait for the flush operation of
cpuset_migrate_mm_wq to complete in cpuset_write_resmask, as modifying
cpuset.cpus or cpuset.exclusive does not trigger mm migrations. The
flush_workqueue can be executed only when cpuset.mems is modified.

Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
---
 kernel/cgroup/cpuset.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 27adb04df675d..3d8492581c8c4 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3256,7 +3256,8 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
 out_unlock:
 	mutex_unlock(&cpuset_mutex);
 	cpus_read_unlock();
-	flush_workqueue(cpuset_migrate_mm_wq);
+	if (of_cft(of)->private == FILE_MEMLIST)
+		flush_workqueue(cpuset_migrate_mm_wq);
 	return retval ?: nbytes;
 }
 
-- 
2.20.1

On Thu, Sep 04, 2025 at 03:45:03PM +0800, Chuyi Zhou wrote:
> It is unnecessary to always wait for the flush operation of
> cpuset_migrate_mm_wq to complete in cpuset_write_resmask, as modifying
> cpuset.cpus or cpuset.exclusive does not trigger mm migrations. The
> flush_workqueue can be executed only when cpuset.mems is modified.
> 
> Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>

Applied cgroup/for-6.18.

Thanks.

-- 
tejun

On 9/4/25 3:45 AM, Chuyi Zhou wrote:
> It is unnecessary to always wait for the flush operation of
> cpuset_migrate_mm_wq to complete in cpuset_write_resmask, as modifying
> cpuset.cpus or cpuset.exclusive does not trigger mm migrations. The
> flush_workqueue can be executed only when cpuset.mems is modified.
>
> Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
> ---
>   kernel/cgroup/cpuset.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 27adb04df675d..3d8492581c8c4 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -3256,7 +3256,8 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>   out_unlock:
>   	mutex_unlock(&cpuset_mutex);
>   	cpus_read_unlock();
> -	flush_workqueue(cpuset_migrate_mm_wq);
> +	if (of_cft(of)->private == FILE_MEMLIST)
> +		flush_workqueue(cpuset_migrate_mm_wq);
>   	return retval ?: nbytes;
>   }
>   

LGTM

Reviewed-by:  Waiman Long <longman@redhat.com>

On Thu, Sep 04, 2025 at 03:45:03PM +0800, Chuyi Zhou <zhouchuyi@bytedance.com> wrote:
> It is unnecessary to always wait for the flush operation of
> cpuset_migrate_mm_wq to complete in cpuset_write_resmask, as modifying
> cpuset.cpus or cpuset.exclusive does not trigger mm migrations. The
> flush_workqueue can be executed only when cpuset.mems is modified.
> 
> Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
> ---
>  kernel/cgroup/cpuset.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Reasonable and AFAICT correct optimization.

Reviewed-by: Michal Koutný <mkoutny@suse.com>